Aqueous solutions containing amino acids and peptides. Part 16.—Solute–solute interactions in solutions containing some N-acetyl-N′-methylamino acid amides

Abstract

The energetics of the interactions occurring between some N-acetyl-N′methylamino acid amides in aqueous solutions at 25 °C have been investigated. Osmotic coefficients and enthalpies of dilution have been obtained for single-component and two-component solute systems for the species N-acetyl-N′-methylglycinamide, N-acetyl-N′-methyl-L-alaninamide and N-acetyl-N′-methyl-L-leucinamide. Enthalpy-of-dilution data were also obtained for the sparingly soluble substance N-acetylglycyl-L-alaninamide. The results obtained have been used to calculate the pairwise free energy and enthalpy coefficients for the homotactic and heterotactic interactions and these are compared with results obtained earlier on some analogous systems containing the primary amino acid amides. A group-additivity approach has been used to rationalise the information obtained. This works tolerably well for most of the systems investigated.